Today, wastewater is disposed of by sewage treatment plants, in which it is mixed with all different kinds of more or less polluted wastewater. The result is that odors are spread and a questionable, and sometimes a hazardous sludge is obtained, which has to be disposed of.
The wastewater from a dairy can amount to 20–30 million liters, which requires large areas for sedimentation basins for settleable solids. Such amounts require the corresponding amounts of raw water. Since water becomes a more and more expensive raw material, its economic effects can not be underestimated. For example, in Saudi Arabia the water costs are SEK 25 per m3. Pure water requires substantial investments.
In modern plants for treating wastewater from dairies gravity thickening is used in order to improve the sedimentation rate, for example by releasing fine air bubbles as in a plant of the type dissolved air flotation (DAF). However, sufficiently pure water can not be obtained with an ordinary plant for wastewater treatment of the DAF type when wastewater from a dairy is treated. Furthermore, this type of water purification does not result in a sufficiently pure water to be reused as a technical water or as a raw water.
With the above-mentioned volumes of wastewater from a dairy an overflow may occur without control and the wastewater may reach small waters which can be very sensitive to this discharge. The average characteristics of the wastewater from a milk processing includes a biochemical oxygen demand (BOD) of about 1,000 mg/l, a chemical oxygen demand (COD) of about 1,900 mg/l, a total solids content of 1,600 mg/l, and a suspended solids content of 300 mg/l. These figures dramatically exceed those permitted by governments in different countries. In Australia for example, the maximum allowable amount of BOD to be discharged to a recipient, such as a river, is 180 ppm.